The present invention generally relates to ink jet recording methods and apparatuses, inks and ink cartridges, and more particularly to an ink jet recording method, an ink jet recording apparatus, an ink and an ink cartridge which are suited for suppressing blending, bleeding or the like so that a high quality recording is possible.
Various kinds of ink jet recording methods have been proposed. For example, in the bubble (or thermal) system, the ink is heated to generate bubbles and the pressure introduced by the bubbles is used to eject the ink. According to the piezoelectric system or the acoustic wave system, a piezoelectric element or an acoustic wave generating element is used to mechanically vibrate or displace the ink so as to eject the ink. In addition, systems which eject the ink from a nozzle using a magnetic field or an electric field have also been proposed. According to these ink jet recording methods, the recording is made by ejecting droplets of ink so that a portion or all of the droplets are adhered on a recording medium. For this reason, no noise is generated during the recording, and it is possible to make color recordings at a high speed.
Normally, the main component of the ink that is used for the ink jet recording is made up of coloring material such as dye and pigment and which is used as the recording agent, and liquid medium. For safety reasons and to obtain a satisfactory recording characteristic, water soluble dye and preferably acid dye or direct dye are used as the recording agent. On the other hand, for safety reasons and to ensure a satisfactory recording characteristic, liquids having water as the main component are used as the liquid medium. In addition, polyhydric alcohol or the like is often added to the liquid medium so as to prevent the nozzle of a head from becoming blocked and to stabilize the ink ejection.
The recording medium that is used by the ink jet recording apparatus includes normal or plain paper such as woodfree copier paper used in copying machines, and paper which is also sometimes referred to as ink jet recording paper (or sheet). The ink jet recording paper is made up of a base and an ink absorbable and/or ink soluble ink receptor layer which is provided on the base. However, because the performance of the ink jet recording apparatus has improved and it is possible to make color recordings at a high recording speed, there are now new demands to be satisfied. Among such new demands, there is a demand to stably fix the ink on the recording medium at a high speed so that the blending or bleeding of the ink is not notable even on the plain paper.
When inks having different colors are mixed at a boundary of the two colors, the blending occurs and the recording quality deteriorates. Hence, various methods have been proposed to suppress this blending, such as the methods (1) through (7) described in the following.
According to the method (1), the boundary tension between the two inks having the different colors and forming the color boundary is set large. This method (1) is proposed in a Japanese Laid-Open Patent Application No.2-175253, for example.
The method (2) makes the diffusibilities of the inks with respect to the recording medium different. The diffusibility of the ink refers to the property of the ink used to indicate the ease with which the ink is diffuses into the recording medium and is absorbed by the recording medium. This method (2) is proposed in Japanese Laid-Open Patent Applications No.4-355157 and No.4-364961, for example.
According to the method (3), no ink is adhered on the color boundary portion to make the color boundary portion void. This method (3) is proposed in a Japanese Laid-Open Patent Application No.3-146355, for example.
The method (4) completes the recording by carrying out thinned recording a plurality of times. This method is also proposed in the Japanese Laid-Open Patent Application No.3-146355, for example.
According to the method (5), an ink repellent agent is coated on the recording medium in advance, so that the inks having the different colors will not make contact at the color boundary by preventing the diffusion and spreading of the ink with respect to the recording medium. This method (5) is proposed in a Japanese Laid-Open Patent Application No.3-002046, for example.
The method (6) reduces the number of ink particles or the amount of ink that is adhered on the color boundary portion.
The method (7) uses a fixing unit which forcibly evaporates the ink that is adhered on the recording medium.
However, according to the methods (1) and (2), the diffusibilities of the inks with respect to the recording medium are different. For this reason, when the recording is made by the ink having the large diffusibility, the bleeding or blur at the edge of the recorded portion becomes large along the fiber of the paper. As a result, the recorded image is not sharp, and there was a problem in that picture quality greatly deteriorates.
On the other hand, according to the method (3), a white unrecorded portion is formed at the color boundary portion in the case where the recording medium used is white paper. Hence, there was a problem in that the picture quality of the image as a whole and the recording tone deteriorate. Particularly at the color boundary portion of dark colors having a large contrast with respect to the white background of the paper, the picture quality deterioration was considerable.
Furthermore, according to the method (4), the number of scans made by the recording head with respect to the recording medium becomes large, and there was a problem in that the recording speed becomes low.
According to the method (5), the size of the dots formed by the ink becomes small, and there was a problem in that the picture quality deteriorates because the recording tone becomes poor and/or the dots become uneven or non-uniform. In addition, the user must use a special recording medium, thereby making it inconvenient for the user.
Moreover, according to the method (6), there was a problem in that the picture quality becomes poor due to deterioration in the resolution at the color boundary portion and the deterioration of the recording tone.
According to the method (7), it is necessary to provide a fixing unit which is relatively large. As a result, there were problems in that the ink jet recording apparatus becomes large and the power consumption increases.
On the other hand, when recording line drawings and general images on the recording medium with a desired resolution by the ink jet recording apparatus, it is necessary to adjust the amount of ink that is ejected from the head so that the obtained dot size is suited for the predetermined resolution. The spreading of the dot on the recording medium is smaller for the ink having the low diffusibility than the ink having the high diffusibility, and the amount of ink recorded on the recording medium is larger for the ink having the low diffusibility as compared to the ink having the high diffusibility. This tendency is notable in the case of copier paper which is subjected to a sizing process or the like which suppresses diffusion of the ink into the recording medium, and plain paper such as bond paper and post card. On the other hand, in the case of ink jet recording paper such as the coated paper exclusively for use in the ink jet recording, overhead projector (OHP) film and glossy paper, the ink acceptor layer is provided on the base paper/film so that the ink absorption is uniform and/or fast. Hence, the effects of the diffusibility of the ink on the ink absorptivity (or permeability) of the recording medium is relatively small in the case of the ink jet recording paper. For example, the ink acceptor layer is made of hydrophilic and water absorbent polymers and resins such as polyvinyl alcohol and cationic resins, pigment, binder and the like.
Therefore, the behaviors of the inks having different diffusibilities on the recording medium greatly differ, and there was a problem in that it is difficult to design a recording medium which guarantees a sufficiently high performance with respect to each of the various inks.
In addition, the diameter of the nozzle of the head is on the order of 50 .mu.m to 100 .mu.m and very small. Hence, a solvent which is non-volatile and hygroscopic is added to the ink so that the ink will not evaporate and dry up at the tip end of the nozzle (nozzle orifice) to block the nozzle orifice. However, although it is possible to prevent blocking of the nozzle orifice caused by the deposition of the dye within the nozzle orifice, the increase of the ink viscosity caused by the evaporation of the solvent cannot be avoided. As the ink viscosity increases, the ink injecting direction becomes unstable, and an error is generated in the position of the dot recorded on the recording medium. In extreme cases, it no longer becomes possible to inject the ink because of the increased ink viscosity, and the dot to be recorded on the recording medium becomes omitted or drops out. In order to prevent these inconveniences, there was a proposal to provide a backup unit and to spray the ink from the nozzle into the backup unit before the ink viscosity becomes too large so as to clear the nozzle orifice. But the ink viscosity depends on the kind and density of the wetting agent, dye and the like included within the ink. Although the ink viscosities of the various kinds of inks used in one ink jet recording apparatus may be different, the conventional ink jet recording apparatus gave absolutely no consideration as to the differences in the ink viscosities among the various kinds of inks.